1. Field of the Invention
The present invention relates to a gas circulation fan for an excimer laser apparatus. More specifically, the present invention relates to a gas circulation fan for an excimer laser apparatus that emits laser, by circulating halogen gas such as fluorine gas.
2. Description of the Background Art
In a conventional excimer laser apparatus, rolling bearing has been used as a bearing for the laser gas circulation fan. Generation of an impurity gas resulting from a reaction between the halogen gas such as fluorine included in the laser gas and bearing lubricant, and generation of dust from rolling surface of the bearing ball, however, degraded laser gas, affecting the laser output. As a solution to this problem, recently, a magnetic bearing has come to be used.
FIG. 6 is a block diagram showing a configuration of a mechanical body unit and a controller of a conventional magnetic bearing apparatus for the gas circulation fan. Referring to FIG. 6, on a main shaft 1, a fan 2 is attached, forming a rotary body 3. Gas 21 is circulated, as fan 2 rotates in a chamber 20. Rotary body 3 has one side pivotally supported by a magnetic bearing 41, and the other side pivotally supported by a magnetic bearing 42. Magnetic bearing 41 on one side includes an electromagnet 51 positioned in a housing 23 and supporting, in non-contact manner, one side of rotary body 3, and a position sensor 61 detecting position of rotary body 3. Magnetic bearing 42 on the other side includes an electromagnetic 52 positioned in a housing 24 and supporting, in a non-contact manner, the other side of rotary body 3, and a position detection sensor 62 detecting the position of rotary body 3.
Magnetic bearings 41 and 42 are connected to a controller 7 through cables 81 and 82, respectively. Controller 7 includes a position detection sensor circuit 9 processing signals from position sensors 61 and 62 and converts an amount of displacement of rotary body 3 to a voltage ratio; an offset adjuster 10 electrically correcting position mechanical deviation from the center of the floating position of rotary body 3; a sensor feedback gain adjuster 11 adjusting gain of an output representing displacement of position detection sensor circuit 9; a filter circuit 12 for reducing bending natural frequency or the like of rotary body 3; a phase compensating circuit 13 for stabilizing control system; and a power circuit 14 supplying current to electromagnets 51 and 52.
In the conventional magnetic bearings 41 and 42 shown in FIG. 6, when a characteristic of mechanical body unit 25 such as a bearing gap or a main shaft natural frequency changes because of variation in processing accuracy, for example, position detection sensor circuit 9, offset adjuster 10, sensor feedback gain adjuster 11 and filter circuit 12 must be finely adjusted to address the change of mechanical body unit 25, and it has been difficult to maintain compatibility between mechanical body unit 25 and controller 7. For example, when controller 7 fails and is exchanged by a new controller, various portions of controller 7 must newly be adjusted. This is very troublesome in adjusting and maintaining the apparatus, and has an influence on productivity of the apparatus.